Just when you thought we had discovered signs of life everywhere possible on Earth, a new expedition has revealed a complete ecosystem existing in the deepest layer of the planet’s crust.

Just when you thought we had discovered signs of life everywhere possible on Earth, a new expedition has revealed a complete ecosystem existing in the deepest layer of the planet’s crust.

A drilling expedition towards the Earth’s centre would mean digging through sediment, a layer of basalt, and then hit the gabbroic layer, which lies directly above the mantle.

A team led by Stephen Giovannoni of Oregon State University in Corvallis drilled down to 1391 metres, where temperatures reach 102 degrees Celsius. Here, they found communities of bacteria that were sparse but widespread, reports New Scientist.

But the type of organisms they came across was very different.

One key difference was that archaea were absent in the gabbroic layer. Also, genetic analysis revealed that unlike their upstairs neighbours, many of the gabbroic bugs had evolved to feed off hydrocarbons like methane and benzene. This could mean that the bacteria migrated down from shallower regions rather than evolving inside the crust.

"This deep biosphere is a very important discovery," said Rolf Pedersen of the University of Bergen, Norway. He added that the reactions that produce oil and gas abiotically inside the crust could occur in the mantle, meaning life may be thriving deeper yet.